A mission to Mars will be mankind's next giant leap.
But one expert has suggested it might be simpler to get to the red planet in a series of smaller jumps - using asteroids as stepping stones.
Professor Richard Binzel of the Massachusetts Institute of Technology is calling for a comprehensive survey of asteroids between Earth and Mars so a plan can be formulated.
"Near-Earth asteroids are the most accessible interplanetary stepping stones to Mars," said Binzel.
"Once humans can reach one asteroid in its native orbit, the gateway is opened such that hundreds, if not thousands more will be accessible.